Covering Indexes

Problem

You want to completely eliminate disk seeks for a specific query by storing all the selected columns directly inside the index structure. Write a query that can be entirely resolved by an index on (last_name, first_name). Retrieve first_name and last_name from employees where last_name = 'King'.

Database Schema

Table: employees

• employee_id (INT): Unique identifier for the employee.
• first_name (VARCHAR): First name of the employee.
• last_name (VARCHAR): Last name of the employee.
• salary (INT): Employee's salary.
• department_id (INT): Foreign key referencing the department.
• manager_id (INT): Foreign key referencing the manager (another employee).
• hire_date (DATE): Date the employee was hired.

Table: departments

• department_id (INT): Unique identifier for the department.
• department_name (VARCHAR): Name of the department.

Try It

Hint

Solution